Prognostic Meteorological Discussion
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FXAK02 KWNH 231832
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ALASKA EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
232 PM EDT SAT SEP 23 2017

VALID 12Z WED SEP 27 2017 - 12Z SUN OCT 01 2017

ENSEMBLE MEANS CONTINUE TO BE IN VERY GOOD AGREEMENT WITH THE
LONGWAVE PATTERN OVER ALASKA DURING THE LATER HALF OF NEXT WEEK,
WHICH SHOULD FEATURE AN ANOMALOUS UPPER LOW LIFTING NORTHEASTWARD
THROUGH THE GULF OF ALASKA WHILE UPSTREAM RIDGING PROGRESSES
THROUGH THE BERING SEA.  THE MEANS MAINTAIN AGREEMENT EVEN INTO
NEXT WEEKEND WITH ADVERTISING RIDGING IN BERING SEA SHOULD
SUPPRESS AND SHIFT EASTWARD AS A LARGE SCALE UPPER TROUGH
APPROACHES FROM THE WEST.

THE 00Z ECMWF MATCHED FAIRLY WELL WITH THE ENSEMBLE MEANS EARLY IN
THE PERIOD, SO THE WPC FORECAST STARTED WITH A BLEND OF THE 00Z
ECMWF AND 00Z NAEFS/EC/GEFS MEANS.  HOWEVER, THE FORECAST BLEND
QUICKLY TRANSITIONED TO ALL ENSEMBLE MEAN GUIDANCE BEYOND DAY
5(THURSDAY) IN ORDER TO ACCOUNT FOR THE CONTINUED RUN-TO-RUN
VARIABILITY IN THE DETERMINISTIC GUIDANCE WITH THE EVOLUTION OF
THE UPPER LOW WHILE IT LIFTS THROUGH THE GULF LATE NEXT WEEK AS
WELL AS THE TIMING DIFFERENCES WITH THE LEADING EDGE OF HEIGHT
FALLS FROM THE LARGE SCALE UPPER TROUGH EDGING INTO THE BERING SEA
NEXT WEEKEND.

IN TERMS OF SENSIBLE WEATHER OVER ALASKA DURING THE DAY 4-8
PERIOD, THERE IS STILL A STRONG SIGNAL THAT A PERSISTENT STREAM OF
MOISTURE AHEAD OF A DEEP SURFACE LOW AND COLD FRONT LIFTING
THROUGH THE GULF WILL BRING HEAVY PRECIPITATION TO THE PANHANDLE
DURING THE MIDDLE OF NEXT WEEK, WITH THE WET CONDITIONS EXPECTED
TO SPREAD INTO THE SOUTHCENTRAL PORTION OF THE STATE.


GERHARDT


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